Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.
Since Boeing sticks to Al for the B777X I doubt a 7 abreast plane would use a carbon fibre fuselage.
An A310 is 46,66m long, 8,3 x diameter.
The B767-200 is 48,51 m long, 9,6 x width, 9,0 x hight.
(B767 fuselage: 17 ft 9 in / 5.41 m height, 16 ft 6 in / 5.03 m width)
Boeing kept to AI on the 777X to be able to use the same production equipment and have it considered as a derivative. Changing the Fuselage material would have been considered a new type I think it is safe to definitively say.
I also think Fred's models - which I believe are assuming that AI is being used for the 2x3x2 is showing that AI would be quite heavy. Complex Carbon structures must be really hard to model requiring very sophisticated models and very powerful computers in order to get the weight to acceptable levels.
What they show is the inherent disadvantages and advantages of different cross sections for different pax capacities in terms of weight. What they absolutely don’t show is that Al is heavy. Carbon structures don’t need magic special computers but complex structures do (I believe you are referring to FEA). Al is chosen because of its more ubiquitous nature and that the reference properties are easier and more reliable to come by. The detailed design choices might be slightly different based on the materials but the drivers as shown in my models are absolutely the drivers for all materials. Computers don’t break physics, even if they are working on magic carbon.
Just out of interest, how much weight did the 787 or A350 save over their Al rivals (A330 &777) by using majority carbon structure?
To save a lot of Grief (and work) - I would suggest that Fred just model Round cross sections using AI of equivalent circumference then we should be able to look at them and make an intuitive guess that if Boeing (or Airbus if they choose to do so) can keep the weight within x% of that AI Round model in a Carbon Ovalish design it could work at that capacity.
Instead of an intuitive guess, why don’t we use the model that is already working? The model is absolutely set up to use ellipses and whilst not an exact representation of the aircraft being mentioned it does provide a closer reflection of reality.
I find it strange however that you suddenly want to go back to modelling it as a cylinder even though that isn’t an issue for my model? I was under the understanding that the raison d'être for your ugly baby was the fact that it absolutely was not a circle
however but now you are seeing that this is hampering it from a weight perspective you want to move away from that? To save grief? I do have to wonder who’s grief is going to be saved...
A 2-3-2 at 168"H ( 4.27M)x 185" W (4.7M) (18" aisles using 777X seat sets and assuming side walls 1" thinner than 777X) and 39.6 M long (13.2M ends) would be 9.27x Height and 8.42X width - somewhere around 8.9x averaged out.
Don’t you worry, I am working on a way to suitably model the available space in the tail whereby the maths takes care of it.
It's not that far out and we know this would never be the shortest variant and possibly not a bad starting point, especially if it is a full clean sheet with 2020's full electric vs 1980's systems architecture and things like a more Aero nose than a probable rewinged A320/321 based competitor to offset that extra 50-100 lbs of fuselage form drag.
Don’t worry, I’ll start an aero thread.
I would assume that a revamped A320 would have equivalent aero in terms of wings/tail and the engines would have similar TSFC - it's just whether or not the regulators would allow that to be certified as a derivative. Given what is happening with 777X which has been a similar development - I'm not sure they would.
The theory behind use of the supplemental type certificate has not changed (unless you have evidence to the contrary) the delay in the 777X as far as I can tell is the result of the realisation of the FAA that their oversight into the process was not suitable and the due diligence was not adhered to suitably.
I have completed the addition of the length calculation utilising the available end space. The model determines at what scaled variant of the cross sectional ellipse a consistently sized shape (consistent across the whole model, between configurations (2m x 2m) will fit. This is then used to determine how far down the tapered cross section space could be used. The tail taper ratio (consistent across all configurations) can then be used to calculate the available area in the tail tapered section (Assuming a trapezoidal shape). The length of the fuselage required for seating is simply the number of seats divided by the number accross to get the number of Rows and then multiplied by the seat pitch
The area required for the ancillary items in the cabin (toilets, galleys, closets etc) are calculated at 0.2m^2 per pax. The available space in the tail is then removed from this figure to leave the remaining constant cross section space to be taken up by the ancillaries. The constant cross sectional ancillary area is then divided by the available width to get the length of the constant cross section required by the ancillaries. This length is then added to the seat Rows X pitch to get the length of the constant section. The constant cross section then has 4 x Ramanujan perimeter based equivalent width added (1.5 nose +2.5 tail).
This is the resulting chart using the above assumptions on length is below ( at 32" pitch)
For reference at 206 seats the A32X cross section is at 43.4m and the Wide oval is at 40.7m